1. Field of the Invention
The present invention relates to an assembly for collecting medical specimens and more specifically, the present invention relates to a cap for a blood collection tube.
2. Description of Related Art
Blood samples and other medical specimens are routinely taken and collected in a specimen collection container. In blood collection applications, the collection container is typically a hollow blood collection tube with one end closed by a semi-spherical portion and the other end open. The open end is sealable by an impervious elastomeric cover. The tube thus defines an interior chamber for collecting and holding the blood sample.
To collect a blood sample, the tube is used in concert with a tube holding device. This device typically comprises a hollow needle extending through the closed end of a tubular housing. The tubular housing has an opposed open end for accepting the blood collection tube. The hollow needle is inserted through the dermal layer into the lumen of the blood vessel and taps into the circulation system of a subject to direct blood therethrough towards the interior compartment of the holding device. The collection container is inserted through the open end of the holder so that the hollow needle punctures through the cover of the collection container. The interior of the collection container is now in direct communication with the circulation system and, having typically been formed in a vacuum, draws blood through the hollow needle and into the collection container. Once the phlebotomist has drawn enough blood into the collection container, the container may be removed from the holder. The container cover, being of an elastomeric material, reseals the hole made by the needle. The phlebotomist may then, if desired, insert a new collection container into the holder to draw more blood.
Some holding devices include a deformable sheath over that portion of the hollow needle extending into the interior of the tubular housing. The sheath covers the entire portion of the needle inside the tubular housing when no blood collection tube is present. When the blood collection tube is longitudinally inserted into the holder, the elastomeric cover of the tube allows the hollow needle to pass therethrough but pushes the sheath back into a compressed position. When the tube is removed from the housing the sheath expands back to cover the hollow needle so that the phlebotomist is not exposed thereto. This spring-like expansion characteristic of the deformable sheath also exerts a force against the cover of the tube, and thereby acts to push the tube out from the housing.
Since the blood collection tube must be maintained in a fixed position within the housing during sample collection, the spring force of the sheath against the tube cover must be overcome.
It is therefore desirable to provide a blood collection tube with improved engagement characteristics for maintaining engagement between the tube and the holding device during sample collection.